Acral lentiginous melanoma, light micrograph. Acral lentiginous melanoma (ALM) is the most common type of melanoma in dark-skinned and Asian populations. The most common locations are the thumb, big toe, and the heel. This is a light photomicrograph ALM arising in the heel of an elderly female. It shows highly pleomorphic tumour cells with hyperchromatic nuclei. Multinucleated giant tumour cells and occasional mitotic figures are also seen.